Simple TV Tuner

[jollyrgr]

In the past I've extracted RF modulators from VCRs, video games, etc. But I have not had to do this in many years as most TVs have a video input.

But a friend has thrown me a challenge. He wants a SIMPLE tuner that has F connector in, composite video, audio output. It does not have to have a number display or any display for that matter. Just a knob that can be tuned to the channel of choice. I'm wanting to extract a tuner from a VCR or get something like this:
http://www.alltronics.com/cgi-bin/categ ... tem=99V016

But my problem is finding any documentation on these. I'm assuming a simple voltage divider is needed. Or do these already have what is needed and only a potentiometer is required to tune them? I recall there were some old TVs and VCRs that had a thumbwheel that you tuned to each channel. Then you pushed a PRESET for each thumbwheel tuned channel.

Anyone have data sheets they can post or link?

[Robert Reed]

Hi Jolly
I think most modern tuners (in the last 25 years) Use a varactor to tune them, however its really a varactor tuned VCO. The varactor is driven by the DC output of a phase locked loop. The individual channel selection is determined by presetting divide by 'N' counters and that is done digitally to put the preset count on them per channel. I don't think you will have an easy time finding a tuner that you merely control with a DC voltage from a potentiometer.

[Externet]

Greetings, jollyrgr
Those tuners from the seventies you mention that had a dozen of 3 position selectors for VHF-lo, VHF-hi and UHF with its corresponding potentiometer can be used, but together with the rest of the receiver disconnecting/eliminating video drivers, vertical and horizontal circuits; in other words a hacked TV mainboard -dump the CRT- to get the video output.
The tuner alone has only 45 MHz IF output, no video.

Rethinking, the whole working tv will give you a monitoring screen of what you are tuning. Just replace one of the tiny potentiometers with a multiturn one. I used a "delay" type one as some oscilloscopes have, the knob has markings from 0 to 1000 in 10 turns.

I have a "Poorman's spectrum analyzer"
http://www.science-workshop.com/
assembled kit, uses one of those tuners. The tiny voltage tuning potentiometer replaced with a repetitive ramp oscillator feeding the tuning voltage and displays on a oscilloscope the entire bands from 2MHz to ~700 MHz.

I did get a TV tuner data sheets from a Sam's? photofact TV service manual at the public library, and will look for it on my pile of documentation and will let you know if I find it, but if you go to the public library may get it faster for the model you may have canibalized on hand.

The divided voltage has to be very stable for manual tuning with a potentiometer, from 0 to 40 volts to sweep the whole spectrum. And thermals do bring it out of tune if the AFC is not engaged. So yes, you can use a multiturn potentiometer as a divider.

I did the same to an old analog cellular telephone and by turning the potentiometer feeding the VFO can hear all the channels. And wow! what is heard there!

Miguel

[Externet]

Found it, jollyrgr.
The schematics on the guts of a tuner VEQS0390 plus IF and video peripherials. I believe I also have that tuner, but will take longer to find.

Can put it on the mail, it's a dozen pages. Contact me at
externet at inorbit dot com, or 1415 656 1185 evenings.
Miguel

[bodgy]

Found it, jollyrgr.
The schematics on the guts of a tuner VEQS0390 plus IF and video peripherials. I believe I also have that tuner, but will take longer to find.

Can put it on the mail, it's a dozen pages. Contact me at
externet at inorbit dot com, or -----------evenings.
Miguel

Miguel, you might want to PM your phone number to jollyrgr rather than publish it on an open forum.

Colin